The last defenders of the free Syrian village of Ain al-Beida were huddling from a biting wind in a Turkish border town. They were still covered with mud from their desperate escape over the mountains.

The previous day, the unit of 50 ragged fighters were driven out of their village by 500 Syrian soldiers backed with tanks. Afterwards, President Bashar al-Assad’s forces burnt the buildings and planted landmines.

"We’ve never seen them fight like that before, they were crazed," said Jamal, a rebel commander, on Saturday. "You shot them and they didn’t drop. They must have been drugged or something."

Many other villages in Idlib province, in the north along the Turkish border, got the same treatment last week. While the world's attention was focused on the horror being inflicted on Homs, where Syrian troops were accused of "medieval barbarity" by David Cameron, President Assad expanded his scorched-earth policy northwards in an apparent bid to destroy the rebel movement altogether.

"There are soldiers everywhere now," said one man who escaped out of Idlib province on Friday night. "They have flooded the countryside, shelling the villages, searching and raiding everywhere."

Witnesses described finding beheaded bodies left in village streets, badly wounded locals trapped in their homes unable to reach hospitals, and bands of militia roaming the countryside. Fears were growing that these armed groups were massacring populations sympathetic to the rebels, although with communications blocked and only a trickle of refugees crossing the snow-covered mountainous frontier, newly sown with landmines, it was impossible to be sure what was really happening.

What was clear, though, was that some of the main rebel enclaves in northern Syria have been overrun, in an area which had been spoken of as a possible rebel stronghold where the Free Syrian Army (FSA) could be trained and equipped.

"It is very dangerous now," said Wasim Sabbagh, 35, a spokesman with the Free Syrian Army. "One of our commanders couldn’t get across the border into Syria, and he is one of the bravest men we have. The Assad forces are everywhere." News of the northern offensive came as government troops ignored international pleas to relax their stranglehold on the Baba Amr district of Homs, the former rebel stronghold that they finally surrounded on Thursday.

Up to 4,000 people have been trapped there for days without access to food, water or medical supplies, yet an aid convoy from the International Committee of the Red Cross (ICRC) was denied access for a second day yesterday.

Syrian commanders on the ground said it was because of fears that the fleeing rebel troops had sown the area with booby traps, although rebel activists claimed the delay was to give the army time to cover up evidence of summary executions carried out in recent days.

"We are not going in today, negotiations continue to try to get in tomorrow," Sean Maguire, a spokesman for the ICRC told The Sunday Telegraph last night. "One of the reasons we were given was the security situation on the ground; we are not in a position to make a judgment on that.

"But since we have not yet been into Baba Amr, we can’t make any assessment of the humanitarian or human rights situation, which is unfortunate as we believe there are pressing needs there."

Meanwhile, diplomatic pressure continued to mount on President Assad. The Foreign Secretary, William Hague, said the Syrian regime’s refusal to allow humanitarian aid into Baba Amr showed how "criminal" it had become. China, which has so far vetoed United Nations Security Council resolutions condemning Damascus, urged both sides to stop fighting and "launch an inclusive political dialogue with no preconditions".

As they did so, members of the FSA who had fought in Baba Amr spoke of the enormity of the military arsenal deployed against them.

"They used more firepower in the last five days than they did in the first three weeks of besieging the city," said Omar al Homsi, a senior FSA fighter who escaped last week to Lebanon. "They were using tanks equipped with rockets with a 3km range, and in the final days they were using multiple rocket lauchers."

Three days before he left, he added, he witnessed a government unit turn against their division. "We found two tanks smouldering, bodies scattered on the ground," he said.

"Intercepting the army’s military frequencies, we heard officers complaining to their superiors in Damascus that their men would not follow orders. They complained that their men were under orders to deploy rockets on a particular area but had refused."

The regime had prepared for the risk of large-scale defections, however. "In the five days of fighting, the regime replaced the battalions fighting us four times. After a day of fighting, they would swap the battalions, their soldiers had to fight for no more than 36 hours."

While a tense calm hung over Baba Amr yesterday, other districts of Homs came under heavy mortar and machinegun fire, adding to fears that the military campaign was being ratcheted up. Further north, the city of Idlib, another major rebel stronghold, also came under shellfire, prompting talk that it was about to become "the next Homs".

"They are slaughtering people," said Mr Sabbagh, the Free Syrian Army spokesman, listing other places that had he said had been attacked. Kafur Nabel, a village famous for its witty banners mocking President Assad, was shelled, while another town, Darkush, was surrounded by tanks. Wounded civilians were trapped and could not reach treatment, Mr Sabbagh said.

One of the most troubling reports was from the village of Kurim, in the hills near the Turkish border, where rebels fear a massacre may have been carried out. The quiet farming hamlet, whose population is Sunni, is surrounded by villages populated by members of President Assad’s fellow Alawite sect. Many Alawites in the area have been armed by the government, which is accused of stirring up sectarian tensions. Mr Sabbagh said nobody had come out of Kurim for several days, although the village was hard to get in touch with as it was cut off from the FSA.

Poorly armed and largely untrained, the rebel fighters have been unable to hold back a sophisticated modern army equipped with tanks and artillery, and which has not hesitated to use firepower, whatever the civilian cost.

Ain al-Beida, a frontier village near the coast, had been a stronghold of the Free Syrian Army for several months, but its defenders were forced out by a fierce attack on Friday.

After six terrifying hours of one-sided battle, the rebel fighters took refuge in the Turkish village of Guvecci, a hilltop town overlooking the border, where they gave an interview to The Sunday Telegraph. The rebels are not welcomed by Turkish locals, one of whom threw a shoe – an insult in the Arab world – as they walked up the town’s main street.

A couple of miles away, across olive groves and pine-scented forest, their comrades had made a camp hidden in woods 200 yards from a Turkish border tower. Syrian soldiers patrolled within sight.

"We will soon be back in Beida," claimed Mazan, 29, a regular army defector, who said he deserted when he was asked to kill civilians.

His colleagues had a few automatic rifles and one rocket launcher. They looked puzzled when asked if there had been any offers of weapons or money from abroad, but seemed confident, despite the defeats the uprising has suffered in the past month. "We can beat Assad’s army. I don’t know how long it will take," he said. "Many of us will be killed, it is true. But we are ready to be martyrs." Until about 10 days ago, much of Idlib province was in rebel hands, with villages defended by ragtag defence forces of lightly armed young men.

The army controlled main roads and some towns, occasionally sending large columns out on missions that could usually be spotted from some distance.

But now, instead of confining their patrols to the main roads, soldiers and thuggish militia men have started attacking villages, stepping up their campaign massively in the past week.

While villages such as Ain al-Beida are small settlements that appear on no maps, the fact the FSA has been able to hold even a speck of Syrian territory has been an important morale booster. Its loss this weekend will be a blow.

The fighters claimed to have killed about 15 Syrian army soldiers, and said only one of their comrades had been injured. He was recovering in a hospital in Antakya, the main Turkish town near the border. From there, the government in Ankara, which last week accused President Assad of war crimes, has allowed rebels to operate discreetly.

Humanitarian conditions in Idlib province have worsened in the past few weeks. Food is in short supply – with many people surviving off dry bread – and power cuts are frequent. There are few doctors because, say the rebels, the regime has targeted them so that fighters and demonstrators cannot receive treatment.

The FSA, which was started by army defectors last summer and has about 15,000 fighters, is short of weapons, leadership and support. As President Assad’s campaign of destruction has been stepped up in the past month, some foreign sympathisers have arrived to help. Last week, Saudi and Kuwaiti benefactors were in Antakya, trying to find Syrians to give cash to. One Kuwaiti businessman said: "They are short of everything, especially weapons. And they have no bullets."

Mr Sabbagh added: "The politicians in the West are arguing about whether to arm us, but they are doing nothing and for the past month 100 people every day have been killed in Syria."

But he remained buoyed by big new demonstrations against the regime across the country on Friday, including in cities such as Aleppo, traditionally a bastion of Assad support. "It is because people feel horrified and angry at what the regime has done to Homs," he said. "It is enough to make a stone cry."

Additional reporting by Ruth Sherlock in Beirut and Magdy Samaan in Cairo